The present invention relates to a pressure measuring and inflation/deflation control system for tires.
Car and tire manufacturers make ever greater attempts to take account of the constantly increasing demands of modern road users for safety, comfort and convenience. This phenomenon is clear from the commonplace nature of numerous types of device which were virtually non-existent barely a few years ago, such as for example airbags, ABS (anti-lock braking system) brakes, ESP (electronic stability program) devices etc.
More recently, tire pressure measuring and/or monitoring devices have become available. By informing the driver simply, reliably and regularly as to the degree of inflation of the tires of his/her vehicle, an improvement is made to safety, fuel consumption, tire service life etc. Such systems generally comprise at least one pressure sensor of a type known per se.
Thus, certain types of pressure sensor (e.g., capacitive or resistive types) are known, for example, which allow measurement of the pressure of a tire at a given time. In general such sensors require an electrical supply to carry out measurements and transmit the information collected. It is known to equip the wheel with a battery. If it is wished to carry out frequent or even continuous pressure measurements, which is indispensable if it is desired to detect puncture of a tire, the battery has to be easily replaceable, since the sensor makes significant demands on the battery, which becomes rapidly discharged. It has to be possible to effect replacement in a simple, quick and cheap manner.
In such a context, problems of reliability are regularly encountered due to the battery's contacts, which have to withstand the most severe of environments. The contacts deteriorate and the supply of electrical energy risks becoming random or unstable, or even being broken off completely.
To remedy this type of situation, non-replaceable batteries are used, which may be incorporated in definitive manner into the electrical circuit, for example by welding. In this way, a more reliable energy supply is achieved. On the other hand, energy consumption has to be restricted, if the life of the battery is to be prevented from being too short. This comes down to supplying the sensors with power on a discontinuous basis. Pressure measurement may for example be performed by sampling at given time intervals. These time intervals have to be as widely spaced as possible, if it is wished, for example, for the life of the battery to correspond as far as possible to the life of a tire, or even the life of the vehicle. Such a situation is not suitable if it is desired to use the pressure sensor to detect a puncture or any other similar type of situation involving a rapid and significant loss of pressure from a tire. This situation is just as inappropriate if it is desired to effect monitoring for example of inflation or deflation thresholds. Using sampling, for example every 30 or 60 seconds, a possible puncture will be detected solely at the time of the next iteration or measurement, i.e., a certain time after the puncture. However, blow-out detection, to be useful, has to be effected within a very short time, indeed virtually instantaneously. Otherwise, the driver will suffer the consequences of the puncture before being informed thereof. These consequences serve as a warning, and it is often too late to respond, especially if the vehicle is travelling at high speed. In the event of inflation or deflation of one or more tires, it is imperative that the monitoring system respond substantially instantaneously, whether to warn the operator that the required threshold has been reached or alternatively to control automatic stoppage of the inflation/deflation system. The only way of ensuring that accurate monitoring of pressure increase or reduction levels is not indispensable, would be to provide very slow pressure variation rates; the thresholds detected late would not then be exceeded by too much. This would, however, render such operations very long and tedious. Furthermore, during inflation there would be a risk of causing overheating of the compressor, which would be under stress for too long.